Origin from Nothing - what does it mean?

I have been following Quantum Cosmology since Hawking's A Brief history of Time first appeared. That inspired me to attempt to drill down to the technical papers involved. I also made use of the book by Hawking and Penrose, The Nature of Space and Time.

Very broadly speaking there seems to be two approaches: quantum tunneling from nothing (Vilenkin and others) and the no boundary proposal (Hawking and others).

About a year ago, there appeared a paper On 'Nothing' by Brown and Dahlen where they discuss what we mean by 'nothing' in Quantum Cosmology. Link . That paper has exposed difficulties with both 'tunneling from nothing' and the 'no boundary' approach.

To quote from the abstract:

the Hawking-Turok instanton does not mediate the quantum creation of a universe.

Interesting article even though I don't buy into the bubble universe proposals its still a decent read.
"nothing" has a variety of descriptive's. I tend to treat them as simply vacuum states. Of which the names applied to each vacuum state depends on the modelling. ie Bunch-Davies vacuum, true/false vacuum etc.

If your interested in other Universe from nothing modelling, you might look into Lawrence R Krauss.

I heard a lecture by Krauss where he said something like 'if you have quantum mechanics you eventually get something rather than nothing'. That presents a problem because if you have quantum mechanics you already have something rather than nothing. Hawking's 'nothing' includes an instanton with a metric, a matter field, and the laws of physics, of course. Other theories of a Universe from 'nothing' also include the existence of instantons.

What might be preferable would be a theory where the Universe, including the laws of physics, would come in to existence from absolutely nothing at all. It seems that might require a model of absolute nothing based on the number zero. We can decompose zero like 0=a + (-a). Such a theory would place constraints on the laws of physics requiring that as t tends to zero (running backwards) everything cancels out and vanishes into absolute nothing from whence it came.

The minute you involve QM you have at the minimal a Planck length state. Assuming QM is correct on the minimal length. The paper you posted also goes into false vacuum which originated by A.Guth. A true nothing would need to have no volume. How does tunneling occur from a zero volume? which in false vacuum =lowest energy state, true vacuum=measured energy state with a barrier between them.

I've read a couple of different methods one such is CDL or Coleman De-Luccia which is mentioned in your article. Here is a statement from this article.

The problem was first addressed by Coleman and De Luccia (CDL) [1], who generalized
the flat space Euclidean bounce formalism [2, 3] for calculating the rate at which true vacuum
bubbles nucleate within a false vacuum. When the relevant mass scales are much smaller
than the Planck mass and the flat spacetime bubble size is small compared to the spacetime
curvature.

the other method is extra dimensions such as string theory.

this paper also goes into both CDL and Hartle-Hawking state although in this one it states the latter is preferred.

I think 'absolutely nothing' isn't a physically describable state. Or may be better it isn't a state at all. So, to proceed from absolute nothingness to something is unphysical, it is creation. If you decompose zero, you just hide it.

I didnt realise that some were thinking that the universe came from absolutely nothing. I thought that the next level up from our universe was populated by a multitude of particles all floating around at randon, each one having the potential to become a universe, just waiting for the equivalent of a photon or other force carrier to impart the energy to kick off inflation in one of them. That is how I was visualising it based on what I had read about multiverse theory.

I think 'absolutely nothing' isn't a physically describable state. Or may be better it isn't a state at all. So, to proceed from absolute nothingness to something is unphysical, it is creation. If you decompose zero, you just hide it.

In the model of an origin from absolute nothing, zero would represent absolute nothing. It can be decomposed as 0=a+(-a). If you want to call it creation then it would be creation without a creator. I think the process can best be understood by running time back to zero. As t tends to 0 broken symmetries become unbroken and everything cancels out and vanishes at t=0, including the very laws of physics. So, the singularity at the origin of things would then be an empty hole of absolute nothing.

As stated previously, this puts a set of constraints on the laws of physics. For example, the various constants of nature would have to work together to ensure the cancellation and vanishing at the origin of things referred to above.

I think the process can best be understood by running time back to zero. As t tends to 0 broken symmetries become unbroken and everything cancels out and vanishes at t=0, including the very laws of physics.

Are you aware of the Planck units? If you argue "by running time back to zero", you should have an imagination about any physical meaning beyond Planck time. Including causality beyond Planck scale.

Are you aware of the Planck units? If you argue "by running time back to zero", you should have an imagination about any physical meaning beyond Planck time. Including causality beyond Planck scale.

I was trying to keep the discussion somewhat simple. By referring to 'running time backward' I was thinking in terms of a movie running backwards. A celluloid movie is a sequence of frames where each frame is the antecedent for the one following. So running a movie backwards means the antecedant frame follows instead of precedes. Running a movie backwards is a fairly common sense idea which should not require much further explanation.

Let's use imaginary time instead. When we look out in space we observe along spatial meridians. Along each meridian is a foliation of copies of S^2. The union of such foliations over all meridians is what we call the visible universe. Near the singularity at the origin of things, the set of meridians constitute 3 dimensional imaginary time. The meridians converge to a singularity which I am suggesting should be viewed as a point of de-compactification (an empty hole) near which broken symmetries become unbroken and all field probabilities converge to zero. This places a set of constraints on the laws of physics.

Then moving along the meridians in the other direction (away from the point of de-compactification) the universe comes into existence out of absolute nothing.

and a snapshot that has been referenced in these forums several times by others:

Leonard Parker
Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53200, USA
E-mail: leonard@uwm.edu
Abstract. I describe the logical basis of the method that I developed in 1962
and 1963 to deﬁne a quantum operator corresponding to the observable particle
number of a quantized free scalar ﬁeld in a spatially-ﬂat isotropically expanding
(and/or contracting) universe. This work also showed for the ﬁrst time that particles
were created from the vacuum by the curved space-time of an expanding spatially-ﬂat FLRW universe. The same process is responsible for creating the nearly scale-invariant spectrum of quantized perturbations of the inﬂaton scalar ﬁeld during the inﬂationary stage of the expansion of the universe…..

Here is a quote I like from Wikipedia. Keep in mind the quantum fluctuations that are grown with accelerated cosmological expansion [dynamic geometry, dynamic spacetime] can be thought of as a mix of 'real and virtual particles' ...which are also field amplitudes...[analogous to the real and imaginary numbers of the Schrodinger wave equation] So complex imaginary numbers and their operators are associated with virtual particles, which cannot be detected, while complex real numbers and their operators are associated with real [detectable] particles.

There is not a definite line differentiating virtual particles from real particles — the equations of physics just describe particles (which includes both equally). The amplitude that a virtual particle exists interferes with the amplitude for its non-existence; whereas for a real particle the cases of existence and non-existence cease to be coherent with each other and do not interfere any more. In the quantum field theory view, "real particles" are viewed as being detectable excitations of underlying quantum fields. .... In this sense, virtual particles are an artifact of perturbation theory, and do not appear in a non-perturbative treatment.

The book by Birrell and Davies is an excellent reference on quantum fields in curved spacetime.

The tricky thing about particle production during inflation is that the terminology in the field took an abrupt turn with the advent of inflation: instead of particle production during inflation, cosmologists refer to the generation of perturbations. The formalism is the same -- but instead of quanta of the inflaton field, the inflationary expansion creates perturbations in the field value of the inflaton across the universe. Much of the modern work on cosmological perturbation theory has been on studying how these perturbations develop into large-scale structure and how they affect the CMB.

I've got a comprehensive reference list on qft in curved space as well as inflationary perturbations if anyone is interested.

I'm always interested lol. Particularly on the modern QFT applications. I've got a decent collection of the original applications such as Parker, Unruh, False vacuum and inflaton field.
So I would enjoy reading current applications

...... instead of particle production during inflation, cosmologists refer to the generation of perturbations. The formalism is the same -- but instead of quanta of the inflaton field, the inflationary expansion creates perturbations in the field value of the inflation across the universe.

The string theory view of this offers a nice physical insight I think: multidimensional spacetime
sets the vibration patterns of strings....particle characteristics....so a dynamic inflationary geometry enables perturbations not seen so much in a static spacetime.....

I think 'absolutely nothing' isn't a physically describable state. Or may be better it isn't a state at all. So, to proceed from absolute nothingness to something is unphysical, it is creation. If you decompose zero, you just hide it.

The word 'creation' suggests the idea of an uncaused first cause. If the Universe came into existence from absolute nothing then, working backwards, we must conclude that everything disappears at t=0 including all matter, the laws of physics, and time itself. So, strictly speaking there is no t=0 but there are values of t>0. Some may see this (the absence of a first instant of time) as a reductio ad absurdum for an emergence from absolute nothing. On the other hand it might point to the Universe as self-generating and self-sustaining without a first instant of time and without a First Cause.

I would recommend reading Charles Seife book "Zero: The Biography of a Dangerous Idea".

My understanding is the word "nothing" and word "zero" get confused as concepts.

The expression: 010.010

The two outer zeros have no definition and mean nothing.
The two enter zeros have definition and mean everything. Everything taken as one thing has no thing contained within it. The two enter zeros are full not empty but instead just overflowing.

The word 'creation' suggests the idea of an uncaused first cause. If the Universe came into existence from absolute nothing then, working backwards, we must conclude that everything disappears at t=0 including all matter, the laws of physics, and time itself. So, strictly speaking there is no t=0 but there are values of t>0. Some may see this (the absence of a first instant of time) as a reductio ad absurdum for an emergence from absolute nothing. On the other hand it might point to the Universe as self-generating and self-sustaining without a first instant of time and without a First Cause.

It's a rather philosophical debate. If there is a physical reason (fundamental laws) for absolutely nothing being unstable, then there is no t = 0, because there is something for ever. Going back in time never ends. In this case it seems meaningless to question a 'First Cause' even related to those laws.

Causality in a linear context requires first cause. On the other hand causality in a cyclical context does not require first cause. Since science is in the dark in respect to 95% of the universe it may be premature to consider first cause at our current level of ignorance. We should know much more about how the universe currently works before we try to determine what existed 14 billon years ago. In my opinion.